REM Rebound Effect (rapid eye movement) is the lengthening and increasing frequency and depth of rapid eye movement sleep that you get after you get some sleep deprivation. When people are prevented from experiencing REM (rapid eye movement), they then take less time to go into REM state. When people can't obtain enough REM sleep, the pressure to obtain REM sleep increases. When the person is finally able to sleep, he will then spend more of the night in REM sleep.
After research connected rapid eye movement with dreaming, and established that it makes up around 20% of your sleep, experimenters decided to deprive test subjects of just REM sleep, to find out its unique importance. Each time a persons electroencephalogram and eye movements showed the start of REM sleep, the experimenter would wake them up for several minutes. As this “dream deprivation” kept going, the tendency to initiate REM increased, and the subjects were woken up more and more times each night. (Many even left the study early.) Finally, after five nights, the subjects, allowed to sleep uninterrupted, showed a big increase in the percentage of sleep devoted to REM: from an average of 19.4% to an average of 26.6%. (The subjects were also anxious, irritable, and hungry.) These effects stayed significant in comparison with a group of people woken up on the same number of occasions each night, at arbitrary times.
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The fact that REM rebound exists shows that the brain needs both sleep and the achievement of specific sleep stages. In some marine animals, like dolphins and fur seals, when just one brain hemisphere gets deprived of REM sleep, just the deprived hemisphere goes into REM rebound. The other hemisphere is unaffected.
REM Rebound Effect is common to people that take certain sleeping aids and it's often seen during the first few nights after patients with sleep apnea get put on Continuous Positive Airway Pressure (CPAP). Alcohol can also impact REM sleep; it suppresses it during the first half of the night, causing a rebound four to five hours after sleep starts. Although alcohol can decrease how long it takes to fall asleep, it causes a disruption in the sleep cycles. REM sleep gets decreased during the first half of the sleep period causing an increased stage 1 sleep in the second half of the sleep period.